Proximity magnetic reed switch assembly



INVENTOR.

Ell/[f 6T flH/MUMHM; JA?

ATTORNEYS Aug. 3, 1965 E. c. DESHAUTREAUX, JR

PROXIMITY MAGNETIC REED SWITCH ASSEMBLY Filed May 28, 1962 FIG. 2

FIG.I

FIG. 5

United States Patent 3,198,992 PRUXIMITY MAGNETIQ REED SWITCH ASSEMBLYEmiie C. Beshautreaux, lira, 2121 4th t., Kenuer, La. Filed May 28,1962, Ser. No. 198,160 4 Slairns. (Cl. 20tl-37) This invention relatesto a new and improved switch assembly, and more particularly, to oneemploying a magnetically biased pair of contacts which can be opened orclosed depending upon the polarity of a magnetic field which envelops aportion of one of said contacts.

Industrial applications of limit and analogous switches involve theiruse for machine control, alarms, signals, and other such functions wherethe approach or passage of a material body must be detected. Very oftenthe type of function required of a switch is that its contacts open whenthe material body passes by its sensing area in one direction, and thenclose when the body returns past the sensing area in the oppositedirection. During the time that the body is not adjacent the sensingarea, the switch contacts must remain in the state determined by thedirection of travel of the body at the last time it traversed thesensing area. This type of function is quite often required of switchesassociated with floats carried by a rising and falling liquid level, orswitches for determining the end limits of travel of machine toolcarriages and the like. There are many other environments, too, where afunction of this nature is essential.

Therefore, it is one object of the present invention to provide a switchcombination wherein the direction of travel of a body past the sensingarea determines the state of the contacts.

Another object of the present invention is to provide a switch assemblywhich incorporates a magnetic pole in one of the switch contacts.

One species of the present invention requires that the body, whosedirection of travel is to be sensed, actually carry magnetic poles ofunlike polarity whose fields selectively determine the open or closedstate of the switch contacts. In this type of switch, the switchcontacts may be actuated and closed by placing one pole on the bodyclose to the switch sensing area. After removal of this one pole thecontacts remain closed until an unlike pole on the body is placed closeto the sensing area for the purpose of opening the switch contacts.Thereafter the switch contacts remain open until said one pole of thebody is again placed adjacent the sensing area. The unlike poles on thebody are so positioned that both are carried past the switch sensingarea for each direction of travel, with the last pole to pass thesensing area determining the state of the switch contacts. In anotherspecies of the invention, the switch sensing area itself contains meansresponsive to the passage of a ferro-magnetic body in order to generatea field of one polarity or the other for changing the switch contactstate. In this alternative embodiment, two pairs of unlike magneticpoles are employed adjacent the sensing area and are positioned suchthat the flux field of one or the other pair is increased due to theproximity thereto of magnetic material comprising or carried by themoving body. The contact state is therefore determined by the polarityof the last strong field produced during the passage of the externalbody adjacent to the switch sensing area.

It is therefore another object of the invention to provide a switchassembly of the type disclosed wherein magnetic means are employed togenerate a field of one or the other polarity in accordance with theposition of magnetic material in the switch sensing area.

These and other objects of the present invention will become apparentduring the course of the following deice scription, which is to be readin conjunction with the drawings, in which:

FIGURE 1 shows the first embodiment of the switch assembly being used inthe environment of liquid level indication;

FIGURE 2 illustrates said first switch assembly being used to indicatethe end limit travel of a machine tool component; 7

FIGURE 3 shows details of the contacts of said first switch embodiment;

FIGURE 4 shows a second embodiment of the invention which includesmagnetic field generating means internal of the sensing area; and

FIGURE 5 shows the preferred magnetic field generating means of saidsecond embodiment.

Referring first to FIGURE 1, there is shown one typical environment inwhich the novel switch assembly may be utilized, but to which it is notrestricted. Reference numeral 10 generally indicates a contact housingwhich includes a sensing area 12 at one end thereof. Cooperativelyassociated with sensing area 12 is a magnet 14 carried by a fioat member16 which in turn rests upon the surface of a liquid body 18 whose levelmay vary. Magnet 14 is held so that its direction of travel acrosssensing area 12 is substantially transverse to the longitudinal axis 20of the switch contact housing 10. The unlike north and south poles ofmagnet 14 will thereupon be carried successively across sensing area 12,but the size of sensing area 12 and the distance between poles N and Sof magnet 14 should be such that only one of these poles is adjacent thesensing area for any position of float 16.

In operation, assume first that the liquid 18 is low so that the northpole N of magnet 14 is positioned below sensing area 12. At this time,it is assumed that the switch contacts inside of housing 10 are open. Ifthe liquid 18 begins to rise, float member 16 is carried upward in thedirection of arrow A such that the north pole N is eventually carriedadjacent the sensing area 12. The contacts inside of housing 10 are sobiased that they remain open when a north pole is adjacent the sensingarea. If the liquid 18 now rises slightly more, north pole N of magnet14 is carried upward and out of proximity with the sensing area, whilethe south pole S of the magnet 14 is brought adjacent to sensing area12. At this time, the contacts inside of housing 10 close and willthereafter remain closed even through liquid 18 rises to a higher leveland carries south pole S upwards and out of proximity with the sensingarea.

Upon return of the surface of liquid 18 to its original level, magnet 14is carried downward in the direction of arrow B and past sensing area12. During this down- Ward direction of travel, the south pole S ofmagnet 14 first passes sensing area 12, but does not affect the closedstate of the contacts. Upon further lowering of the liquid surface, thenorth pole of magnet 14 is now brought adjacent sensing area 12 and inturn causes the contacts in housing 10 to open. If the liquid levelretreats even more, thus carrying fioat member 16 down further so thatmagnet 14 is completely beneath sensing area 12, the contacts remainopen even though the north pole N of magnet 14 is no longer in proximitythereto. Thus, it is seen that when magnet 14 moves in the direction ofarrow A completely across sensing area 12, the contacts are forcedclosed, whereas upon return of magnet 14 completely across sen-sing area12 in the direction of arrow B, the switch contacts are open.Furthermore, the contacts in housing 10 remain in either the open orclosed state as determined by the last direction of travel of floatmember 16. The closing of the switch contacts and housing 10 may close acircuit leading to an indicator for showing that the liquid level hasrisen above a certain a point, or the contacts may energize a circuitfor automatically controlling the liquid level.

The invention may also be employed in the environment of FIGURE 2. Here,a machine tool carriage 22 is moved in either direction by aconventional rotating lead screw 24 driven by a motor 2-5. Unlikemagnetic poles N and S are positioned at the ends of the carriage asshown. The contact housing 10 is located on the bed so that its sensingarea 12 will be traversed by each of the poles N and S during eachcomplete travel of the carriage in either direction A or B. The openingor closing of the contacts in housing ill can be utilized to determinethe end limits of travel of the machine tool carriage in order toreverse direction of screw thread 24- when an end limit has beenreached. For example, assume that when the contacts in housing in areopen, a relay 2 3 is de-energized so that armature 3G is in the positionshown to thereby supply power to motor as in order to drive machine toolcarriage 22 in the direction of arrow A. The south pole S at the rightend of 22 will eventually come into proximity with sensing area 12 so asto close the contacts, which in turn remain closed even though southpole S is carried a bit beyond to the left of sensing area The closingof contacts in housing it) energizes relay 23 which in turn allowsarmature 36 to apply power for reversing the rotation of motor 245 andthus carry machine tool carriage 22 back in the direction of arrow B.The south pole S is first carried across sensing area in this returndirection but does not ailect the closed position of the contacts inhousing it). Eventuall, carriage 22. moves all the Way to the right sothat the north pole N is brought adjacent to sensing area 12. At thistime, the contacts in housing 10 are opened by the proximity of northpole N in order to again de-energize relay 2% and thus cause machinetool carriage 22 to commence again its travel to the left. It will beseen that, in reality, the environment of FIGURE 2 is analogous to theenvironment of FIGURE 1, except for the fact that the unlike magneticpoles I and S are spaced apart much further in FIGURE 2 than in FIGURE1.

FlGURE 3 illustrates the preferred construction of the switch utilizedin the environments of FIGURE 1 and FIGURE 2. A pair of reed contacts 32and 34 made of spring magnetic material are located in a glass enclosurewhich is hermetically sealed with glass-to-metal seals at the pointswhere the contacts emerge from the glass wall. The glass enclosureitself may be filled with a non-conducting gas so that no current flowswhen the contacts open and an EMF. impressed across the contacts.Conductors 38 and 4%) are mechanically and electrically connected totheir respective contacts 32 and 34 and extend through the hollowinterior of a mounting conduit 42 in order to provide access to theexternal electrical circuit that they are controlling. Conduit 42; hasexternal threads and is placed in a plastic potting compound 44 prior tothe setting of the compound but after it has been poured. The plasticcompound 44 actually provides a case or housing it) for the glassenclosure 36 with the latter being potted therein. Other kinds ofhousings may be provided. A lock nut 46 is also shown having internalthreads that are engaged to the external threads of conduit 42. Thislock out may have hats to accommodate a Wrench to facilitate theconnection of conduit 42 to an external supporting object. The lowerface of lock nut as is in contact with the plastic potting material 44,which greatly improves the mechanical bond between conduit 42 andcompound 44.

The sensing area 32 is located or delineated on housing it} at aposition nearest the fixed end of contact 32. The free end of contact 32is used for engaging the free end of contact 34. A magnetic pole of somepolarity is physically placed or otherwise induced in the free end ofcontact In FIGURE 2, this pole in the engaging end of contact 34 is anorth pole N, but could as well be a south pole. If reed contacts 32 and34 are of a standard unmagnetized type which are purchased alreadyenclosed in container 36, then this north pole N may be convenientlyestablished by incorporating a small biasing magnet -S into the housing13. Biasing magnet 43 is positioned so that its north pole N is adjacentto the fixed end of contact 34, and it is securely held in place by thesurrounding potting compound The flux from north pole N of biasingmagnet 48 traverses a part of contact 34 before returning to the southpole S of magnet 48. This causes a north pole N to be induced in thefree end of contact 34 due to the orientation of the magnetic dipolescaused by the biasing magnetic field.

The contacts 32 and 3d are made of spring material which normallymaintains their free ends out of contact with one another in the absenceof a sufficiently strong threading magnetic field. The strength of themagnetic pole N in the free end of contact 34 should be insul'licientto, by itself, overcome this spring bias. However, once contacts 32 and3d close by the action of some external field, then the strength of poleN in the preferred embodiment should be sufficient to maintain closureuntil some positive step is taken to cancel its ellect.

By bringing a south pole into proximity with sensing area 12 of housingAl, in a manner typically shown in ither FIGURE 1 or 2, the magneticdipoles in contact 32 are oriented so that its free end becomeseffectively a south pole S. The field he ween the free ends of contacts32 and now increases to overcome the spring bias, thus forcing orattracting the free ends of contacts 32 and 3 together. When theexternal south pole is removed from the proximity of sensing area 12,the strength of the north pole N in contact 34- is sufiicient tomaintain the contacts closed. it an external north pole is now broughtinto proximity with sensing area 12, then the di ole orientation incontact 252 is reversed, thus establishing a north pole in the free endof contact 32 which thereupon forces apart said ends. As a slightmodification of FIGURE 3, the normal field of the north pole N incontact can be reduced to a value less than that necessary to even holdthe contacts closed. Thus, the contacts close only when a south pole ismaintained in proximity to the sensing area.

FlGURE 4 shows an alternative embodiment of the present invention inwhich a moving body 5t) carries a body of magnetic material 52 which ofand by itself does not produce a magnetic field. instead, switch contacthousing 54 has included therein magnetic field generating means 56, inaddition to the other elements already described in connection withFIGURE 3. Corresponding numerals in FIGURES 3 and 4 identifycorresponding parts. Magnetic field generating means 5i comprises, inits preferred form, a ceramic material magnet formed generally in theshape of a thin bar or wafer by pressing ceramic powder in a fashionwell known in the art. The rectangular shape of this water is shown bestin FIG URE 5. An aperture 51"; is provided in water 56. A ceramic wafermagnet of the type disclosed may be permanently magnetized so as to forma pair of unlike poles on each of its two major parallel faces, whichare those faces between which aperture 53 extends. As shown in FIG- URE4, a pair of unlike poles S and N is formed on either side of aperture58 at the major face of the Wafer which is adiacent or closest to thehousing sensing area 12. In addition, a pair of auxiliary poles N and Sis formed on either side of aperture 58 on the opposite major face ofwater 56, which is that surface adjacent or closest to the fixed end ofcontact 32. The strength of the auxiliary poles N and S is normally lessthan the strength of the main poles S and N. A magnet of this type showsa strong magnetic attraction from the major poles, but practically nomagnetic attraction from the auxiliary poles. However, it the piece offerro-magnetic material 52 is brought into proximity to'the main southpole S, the field from the auxiliary north pole N increases due to thedecrease in reluctance of the magnetic circuit between poles S and N. Insimilar fashion, if the magnetic material 52 is brought into proximitywith the main north pole N, the field from the auxiliary south pole Sincreases because of the decrease in reluctance of the magnetic pathbetween poles N and S. Thus, a strong field of one polarity or the othercan be selectively generated, according to the position of material 52,to envelop the fixed end of contact 32. This field in turn generates asimilar pole at the free end of contact 32 in order to either close oropen contacts 32 and 34. The arrangement of FIGURE 4 thereby eliminatesthe need for a moving body 50 to carry magnetic poles thereon. Instead,only the external magnetic material 52 is required to selectively varythe reluctance of the paths between the unlike poles in each of thepairs SN or N-S. It should also be noted that the length of material 52may even be of a size so that it is, for some position, in proximitysubstantially with both of the main poles S or N. For this case, whenmagnetic material 52. is moving from left to right, the contacts willnot close until its trailing edge is in proximity with main pole N. Whenonce the switch closes, it remains locked in until the material 52reverses direction, with the contacts opening at least by the time thatits trailing edge moves into proximity with main pole S. if the switchcontacts are open and the material is moved from right to left, theywill first close and then open.

A premagnetized ceramic wafer magnet assembly particularly suitable foruse in the embodiment of FIGURE 4 is termed Index 1 and is made from anon-oriented barium ferrite material which is pressed into the shape ofa thin wafer having a center hole. The dimensions in inches of thiswafer are: length 1.00; width 0.75; thickness 0.177; hole diameter0.137. However, instead of forming the poles S, N, S and N on the samephysical body, it would also be possible to fabricate the housing ofFIGURE 4 using two separate but parallel bar magnets, one with poles Sand N, and the other with poles N and S.

While preferred embodiments of the present invention have been shown anddescribed in detail, it is obvious that many modifications thereto maybe made by persons skilled in the art without departing from the spiritof the invention as defined in the appended claims.

I claim:

l. A switch assembly which comprises:

(a) a pair of cooperating electrical contacts, at least one of which ismade of magnetic material having spaced apart first and second portions,said second portion being adapted to either make or break electricallywith at least a portion of the other contact of said pair;

(b) first means to normally bias open said contacts;

(c) second means establishing a magnetic pole of one polarity in saidother contact at its said portion, said pole having a field strengthwhich, by itself, is insufficient to overcome said bias and close saidcontacts, but which is sufiicient to maintain said contacts closed aftersaid bias has been overcome; and

(d) control mechanism for selectively enveloping said one contact firstportion with either a like or an unlike magnetic field of sufficientstrength so that said second portion thereby is either repelled from orattracted to close with said other contact portion, respectively, wheresaid control mechanism comprises a first pair of spaced apart unlikemagnetic poles each permanently located adjacent to said one contactfirst portion so as to envelop same with a magnetic field, a second pairof spaced apart unlike magnetic poles each permanently located oppositean unlike pole of said first pair so that a flux path is createdtherebetween whose normal reluctance is such as to cause the field fromthe associated pole of said first pair to be of a strength insufficientto affect the state of said contact pair, and a body of magneticmaterial relatively physically movable with respect to said one contactfirst portion which can be selectively moved into the field of eitherone of the poles of said second pair so that the reluctance of itsassociated flux path decreases which in turn increases the fieldstrength of the associated pole of said first pair of poles to therebymake or break said contacts.

2. A switch assembly which comprises:

(a) a housing;

(b) a pair of first and second cooperating electrical contactsinternally placed in said housing, each of which is made of springmagnetic material in the shape of a reed having spaced apart first andsecond portions with said that portion being fixed and said secondportion being adapted to move so as to make or break with the secondportion of the other contact, where said spring nature of each Contactnormally biases open said contacts;

(0) means establishing a magnetic pole of one polarity in said secondcontact at its said second portion, said pole having a field strengthwhich, by itself, is instillicient to overcome said spring bias andclose said contacts, but which is sufficient to maintain said contactsclosed after said spring bias has been overcome;

(d) a sensing area delineated on said housing at a position which isnearest said first contact first portion; and

(e) control mechanism for selectively enveloping said first contactfirst portion with either a like or an unlike magnetic field ofsutficient strength so that said first contact second portion thereby iseither repelled from or attracted to close with said second contactsecond portion, where said control mechanism comprises a first pair ofspaced apart unlike magnetic poles each permanently located within saidhousing at its sensing area position and adjacent to said first contactfirst portion so as to envelop same with a magnetic field, a second pairof spaced apart unlike magnetic poles each permanently located withinsaid housing adjacent to said sensing area and opposite the unlike poleof said first pair so that a flux path is created therebetween whosenormal reluctance is such as to cause the field from the associated poleof said first pair to be of strength insutlicient to affect the stateor" said contact pair, and a magnetic material body external to saidhousing and relatively physically movable with respect to said sensingarea which can be selectively moved exclusively into the field of saidsensing area of either one of the poles of said second pair so as todecrease the reluctance of its flux path associated with the unlike poleof the first pair to thereby increase the field of the unlike first pairpole to a strength sufiicient to affect the state of said contact pair.

3. A combination according to claim 2 wherein said first pair of polesis permanently formed on one face of a water of ceramic magneticmaterial and said second pair of poles is permanently formed on anopposite parallel face or" the same said wafer.

4. A switch assembly according to claim 2 wherein said external magneticmaterial body is relatively movable, with respect to said sensing area,in a path which in turn is substantially parallel in the vicinity ofsaid sensing area to the length of the reed comprising said firstcontact.

References Cited by the Examiner UNITED STATES PATENTS 2,877,361 3/59Chase 20087 2,902,558 9/59 Peek 200-457 2,973,414 2/61 Eossemeyer 200-563,009,033 11/61 Werts 20087 3,011,036 11/61 La Rocca 20087 3,012,11612/61 Boylan et al 200-87 3,046,370 7/62 Adams et al. 20093 BERNARD A.GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

1. A SWITCH ASSEMBLY WHICH COMPRISES: (A) A PAIR OF COOPERATINGELECTRICAL CONTACTS, AT LEAST ONE OF WHICH IS MADE OF MAGNETIC MATERIALHAVING SPACED APART FIRST AND SECOND PORTIONS, SAID SECOND PORTION BEINGADAPTED TO EITHER MAKE OR BREAK ELECTRICALLY WITH AT LEAST A PORTION OFTHE OTHER CONTACT OF SAID PAIR; (B) FIRST MEANS TO NORMALLY BIAS OPENSAID CONTACTS; (C) SECOND MEANS ESTABLISHING A MAGNETIC POLE OF ONEPOLARITY IN SAID OTHER CONTACT AT ITS SAID PORTION, SAID POLE HAVING AFIELD STRENGTH WHICH, BY ITSELF, IS INSUFFICIENT TO OVERCOME SAID BIASAND CLOSE SAID CONTACTS, BUT WHICH IS SUFFICIENT TO MAINTAIN SAIDCONTACTS CLOSED AFTER SAID BIAS HAS BEEN OVERCOME; AND (D) CONTROLMECHANISM FOR SELECTIVELY ENVELOPING SAID ONE CONTACT FIRST PORTION WITHEITHER A LIKE OR AN UNLIKE MAGNETIC FIELD OF SUFFICIENT STRENGTH SO THATSAID SECOND PORTION THEREBY IS EITHER REPELLED FROM OR ATTRACTED TOCLOSE WITH SAID OTHER CONTACT PORTION, RESPECTIVELY, WHERE SAID CONTROLMECHANISM COMPRISES A FIRST PAIR OF SPACED APART UNLIKE MAGNETIC POLESEACH PERMANENTLY LOCATED ADJACENT TO SAID ONE CONTACT FIRST PORTION SOAS TO ENVELOPE SAME WITH A MAGNETIC FIELD, A SECOND PAIR OF SPACED APARTUNLIKE MAGNETIC POLES EACH PERMANENTLY LOCATED OPPOSITE AN UNLIKE POLEOF SAID FIRST PAIR SO THAT A FLUX PATH IS CREATED THEREBETWEEN WHOSENORMAL RELUCTANCE IS SUCH AS TO CAUSE THE FIELD FROM THE ASSOCIATED POLEOF SAID FIRST PAIR TO BE OF A STRENGTH INSUFFICIENT TO AFFECT THE STATEOF SAID CONTACT PAIR, AND A BODY OF MAGNETIC MATERIAL RELATIVELYPHYSICALLY MOVABLE WITH RESPECT TO SAID ONE CONTACT FIRST PORTION WHICHCAN BE SELECTIVELY MOVED INTO THE FIELD OF EITHER ONE OF THE POLES OFSAID SECOND PAIR SO THAT THE RELUCTANCE OF ITS ASSOCIATED FLUX PATHDECREASES WHICH IN TURN INCREASES THE FIELD STRENGTH OF THE ASSOCIATEDPOLE OF SAID FIRST PAIR OF POLES TO THEREBY MAKE OR BREAK SAID CONTACTS.